(1) Field of the Invention
The instant invention relates to a stent for ostial lesions and vascular bifurcations the extremities of which allow a side unfolding totally covering such lesions.
(2) Prior Art
As already known, the most used endovascular treatments at present are those carried out through the interior of the clearance of vascular conduits, instead of using the traditional method of accessing such conduits by means of a surgery allowing access to the affected artery or vein.
Such endovascular treatments are effected into the vessel clearance, with different purposes and using different means, as follows:                to produce dilatation of the artery or vein,        to dissolve thrombi inside the artery or vein,        to close abnormal communications between these vessels, between such conduits or communication to neighbor tissues,        to coat surfaces thereof with a prosthesis, such as a “sleeving”,        to return the normal gage to a dilated artery (aneurysm),        to insulate the inner surface of an artery from blood physical or chemical elements, after effecting a balloon dilatation (inner “bypass”), etc.        
Based on the work of US radiologist Charles Dotter, and within endovascular techniques, endovascular placing of expanders has been an important improvement, specially permeable and resilient tubular structures normally known as “stents”.
Therefore, in the present specification, the term “stent” is applied to those devices which may be also referred to as endovascular “expanders”.
The “stents”—generally made from special metallic frameworks—form expansible skeletal tubes, generating radial forces capable of maintaining the vessels open and counteracting tensions tending to close them.
Essentially, it may be said that there are three kinds of vascular “stents”:: thermo-sensitive stents, which adopt predetermined shapes at different temperatures, particularly that of the human body (as those of Nitinol series; of U.S. Pat. No. 4,425,908, etc.); expansible stents with balloon (such as disclosed in European Patent EP 378,151); and resiliency auto-expansible stents (as disclosed in U.S. Pat. No. 4,580,568).
Vascular “stents” are being used in angioplasty (with increasing frequency) thus attaining an improvement in the immediate and long term results; for treating dissections after angioplasty and for assuring endoluminal grafts, as well as improvement in the quality of various prosthetic applications, (Perrone, R et al, “Prótesis endoluminal” (Endoluminal Prosthesis), Rev. Arg. de Cirugía”, 1992; 62:146-149; Mazzariello, R: “Aplicación percutanea de prótesis biliar expandible” (Percutaneous application of expansible bile prosthesis), Revista Argentina de Cirugía, 1990: 979-983; etc.)
Besides, combined stents or expanders and grafts have been used in several applications, such as: aneurysms, dissections, vascular trauma and arterial occlusion diseases.
Calcified arteries represent a serious problem for intervening cardiologists trying to dilate such arteries by placing stents. Also, there is an important percentage of failures in the results expected from this kind of operations.
More particularly, cases of lesions such as arterial lesions and bifurcation lesions are till now a challenge for interventionalcardiologists or other specialists working in the field of angioplasties.
In fact, the percentage of failures and re-stenosis is very much higher than that obtained with these treatments in other vascular territories. This is due to the fact that expanding devices such as stents, which properly cover ostial or bifurcation zones in the arterial tree have as yet not been developed.